As a valve opening and closing timing control apparatus having the configuration described above, JP 2008-038886A (Reference 1) discloses a technology of a differential speed reduction mechanism in which a ring gear (an internal toothed gear in Reference 1) is disposed coaxially with a rotation axis, an inner gear (a planetary gear in Reference 1) is disposed coaxially with an eccentric axis, which has the posture parallel to the rotation axis, a portion of an external toothed portion of the inner gear is engaged with a portion of an internal toothed portion of the ring gear, and a drive shaft (a planetary carrier in Reference 1) is fitted into the inner gear.
In this technology, a biasing member (a spring member in Reference 1) is disposed so as to be fitted into a region of the outer periphery of the drive shaft that corresponds to the area in which the external toothed portion of the inner gear is engaged with the internal toothed portion of the ring gear. Thereby, a biasing force is applied to the direction in which the internal toothed portion and the external toothed portion are engaged with each other. In particular, Reference 1 describes that a biasing direction of the biasing member is set so as to offset a fluctuation torque applied from an intake valve.
In the configuration described in Reference 1, the biasing force of the biasing member is set so as to allow the ring gear and the inner gear to maintain the engaged state thereof against an engagement reaction force. Thus, the internal toothed portion and the external toothed portion come into strong contact with each other, which increases engagement loss.
In addition, in a configuration in which the outer periphery of the drive shaft is brought into contact with the inner periphery of the inner gear over a long area, the frictional resistance of the contact area is increased by the biasing force of the biasing member. For this reason, when the electric actuator is driven, the rotational speed is suppressed, causing deterioration in responsiveness, and there is room for improvement.
Thus, a need exists for a valve opening and closing timing control apparatus which is not susceptible to the drawback mentioned above.